Monday, 8 April 2013

The Ozone Layer

The Ozone Layer

Ozone is a gas that occurs naturally in our atmosphere. Most of it is concentrated in the ozone layer, a region located in the stratosphere several miles above the surface of the Earth. Although ozone represents only a small fraction of the gas present in the atmosphere, it plays a vital role by shielding humans and other life from harmful ultraviolet light from the Sun. Human activities in the last several decades have produced chemicals, such as chlorofluorocarbons (CFCs), which have been released into the atmosphere and have contributed to the depletion of this important protective layer. When scientists realized the destructive effect these chemicals could have on the ozone layer, international agreements were put in place to limit such emissions. As a result, it is expected that the ozone layer will recover in the coming decades.

Ozone is also a greenhouse gas in the upper atmosphere and, therefore, plays a role in Earth's climate. The increases in primary greenhouse gases, such as carbon dioxide, may affect how the ozone layer recovers in coming years. Understanding precisely how ozone abundances will change in a future with diminished chlorofluorocarbon emissions and increased emissions of greenhouse gases remains an important challenge for atmospheric scientists in NOAA and other research centers.

Ozone Research

NOAA Research has, for many years, played a vital role in studying the ozone layer. For instance, at the Chemical Sciences Division of ESRL, researchers are conducting laboratory and field experiments and designing computer models to study this issue. One of the primary missions of ESRL's Global Monitoring Division is to observe and understand the ozone layer through accurate, long-term measurements of ozone, chlorofluorocarbons, greenhouse gases, and solar radiation.

Taking Observations

NOAA researchers build and deploy instruments all over the world to measure ozone, as well as the trace gases and aerosol particles that affect its abundance. They also participate in many field experiments to study and document the processes that control atmospheric ozone. Research scientists take ozone measurements using instruments located on the ground and onboard aircraft, balloons, and satellites. The data from these instruments provide precise measurements that can be used to detect small regional ozone changes over long periods of time, provide global maps of ozone amounts and examine local ozone distributions.

Ozone Depletion

Antarctica

Ozone depletion occurs in many places in the Earth's ozone layer, most severely in the polar regions. NOAA scientists have traveled to Antarctica to study the ozone hole that has been occurring there since the late 1970s. In 1986, soon after the reported discovery of the ozone hole, Aeronomy Lab (now ESRL) scientist Dr. Susan Solomon led a team of 16 scientists, the National Ozone Expedition (NOZE I), to Antarctica. The scientists took measurements of various trace gases and physical properties of the atmosphere. The data, along with additional findings from the NOZE II mission the following year, showed conclusively that human-produced trace gases that contain chlorine and bromine were causing the ozone hole. The Global Monitoring Division of ESRL has monitored the yearly Antarctic ozone hole since 1986 by launching balloon-borne ozonesondes, from the South Pole station and measuring total column ozone from a ground based Dobson spectrophotometer since 1963.

This unique record from the South Pole station clearly shows the annual development of the springtime Antarctic ozone hole over the past two decades. Ozone depletion at the South Pole can also be viewed from another perspective through the images created from data collected by the NASA TOMS satellite, and the NOAA SBUV-2 instruments aboard NOAA satellites. These various ozone measurements provide an important record of the status of the ozone hole. Continued surveillance is necessary in order to verify the expected recovery of the ozone layer.

Arctic Ozone

Significant depletion also occurs in the Arctic ozone layer during the late winter and spring period (January - April). However, the maximum depletion is generally less severe than that observed in the Antarctic, with no large and recurrent ozone hole taking place in the Arctic.

Since the 1980's, scientists at ESRL have been participants in field, theoretical, and laboratory research to demonstrate some of the key processes that contribute to the observed difference between the depletion of ozone in the Arctic and Antarctic. For example, the POLARIS mission in 1997, was designed to study ozone photochemistry in the Arctic during the summertime at middle and high latitudes. And later, the SAGE III Ozone Loss and Validation Experiment (SOLVE) campaign was designed to examine the processes controlling ozone levels at mid- to high latitudes in the Arctic during the winter. The mission also acquired correlative data needed to validate the Stratospheric Aerosol and Gas Experiment (SAGE) III satellite measurements that are used to quantify high-latitude ozone loss. Both these experiments took measurements using the NASA DC-8 and ER-2 aircraft, as well as balloon platforms and ground-based instruments

Atmospheric Models

Another NOAA lab involved in studying stratospheric ozone depletion is the Geophysical Fluid Dynamics Laboratory (GFDL) in Princeton, N.J. GFDL seeks to understand and predict the Earth's climate and weather, including the impact of human activities. Specifically, GFDL conducts leading-edge research (i.e., atmospheric chemistry modeling) on many topics of great practical value, including stratospheric ozone depletion. For example, the GFDL group developed a 3-D atmospheric model tailored to study the interaction of chemistry, dynamics, and radiation in the stratosphere. Their extensive calculations were necessary for evaluating the simpler models used in the policy assessment studies, as well as for understanding the climatic impact of the Antarctic ozone hole.

Ozone-Depleting Substances

Certain industrial processes and consumer products result in the atmospheric emission of ozone-depleting gases. These gases contain chlorine and bromine atoms, which are known to be harmful to the ozone layer. Important examples are the CFCs and hydrochlorofluorocarbons (HCFCs), human-produced gases once used in almost all refrigeration and air conditioning systems. These gases eventually reach the stratosphere, where they are broken apart to release ozone-depleting chlorine atoms. Other examples are the halons,which are used in fire extinguishers and which contain ozone-depleting bromine atoms.

Methyl bromide, is another important area of research for NOAA scientists. Primarily used as an agricultural fumigant, it is also a significant source of bromine to the atmosphere. Although some ozone-depleting gases also are emitted from natural sources, emissions from human activities exceed those from natural sources.

NOAA researchers regularly measure ozone depleting gases in the lower and upper atmosphere and attempt to account for observed changes. As a result of international regulations, ozone-depleting gases are being replaced in human activities with "ozone-friendly" gases that have much reduced potential to deplete ozone. NOAA researchers are also measuring these "substitute" gases as they accumulate in the atmosphere. Observing changes in both old and new gases emitted into the atmosphere allows researchers to improve our understanding of the fate of these gases after release and thereby improve our ability to predict future ozone changes.

Communicating Information on Ozone depletion

The world's population is a stakeholder in decisions that limit the emissions of ozone-depleting gases. In 1987, the international community put in place a treaty known as the Montreal Protocol on Substances that Deplete the Ozone Layer . Since that initial treaty was ratified, periodic assessments and updates have been conducted. The Protocol success has derived in part from these scientific updates on the science and observation of ozone depletion made over the past 15+ years. NOAA researchers from several laboratories have participated in all of these scientific updates and have also been active in preparing outreach documents to communicate the science of ozone depletion to the public